Ah yeah that’s an issue with the gba itself basically. You can have up to 128 sprites at once, so depending on how long the snake is (each segment has one sprite) and how much text is on screen (it also uses sprites) you can basically just run out.
So the issue is that you basically just got the snake long enough that the gba simply can’t display it anymore. If you also just get it more than 128 segments long the same thing happens.
Wish I could fix it, there are a couple workarounds but they’re a bit out of scope for me unfortunately